How does God's institution of the rainbow in Genesis 9 work?

God could have brought a rainbow especially for the occasion, or it could be that, as at all times when rains come, there was mist in the atmosphere, and God took advantage of the natural rainbow and said, I am using this water and light because I know it will make a rainbow, and I will use the rainbow as the sign of the covenant between man and God. Either way it does not matter; it could be miraculous or it could be natural. Sometimes we just do not know with God, and it makes no difference, because at the end of the day He made a covenant and gave us a sign.